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Cash, Cash Equivalents and Marketable Securities (Details) (USD $)
In Thousands, unless otherwise specified
Jul. 31, 2013
Jul. 31, 2012
Cash and Cash Equivalents and Marketable Securities [Line Items]    
Cost $ 63,631 $ 140,112
Unrealized Gains      
Unrealized Losses Less Than 12 Months      
Unrealized Losses 12 Months or Longer      
Estimated Fair Value 63,631 140,112
Cash
    
Cash and Cash Equivalents and Marketable Securities [Line Items]    
Cost 47,675 96,779
Unrealized Gains      
Unrealized Losses Less Than 12 Months      
Unrealized Losses 12 Months or Longer      
Estimated Fair Value 47,675 96,779
Money Market Funds
    
Cash and Cash Equivalents and Marketable Securities [Line Items]    
Cost 15,956 43,333
Unrealized Gains      
Unrealized Losses Less Than 12 Months      
Unrealized Losses 12 Months or Longer      
Estimated Fair Value $ 15,956 $ 43,333